Question: If a tank can be filled by a pipe in 3 hours and emptied by another pipe in 5 hours, how long will it take to fill the tank if both pipes are opened together?
Options:
Correct Answer: 2.5 hours
Solution:
The combined rate is (1/3 - 1/5) = (5-3)/15 = 2/15. Therefore, it will take 15/2 hours or 7.5 hours.